1. Field of the Invention
The present invention relates to a rubber composition. More specifically, it relates to a rubber composition containing an amorphous or low crystalline ethylene-.alpha.-olefin copolymer rubber and a liquid ethylene-.alpha.-olefin random copolymer and having an excellent processability, thermal aging resistance and wear resistance, which is particularly usable for general rubber articles such as a belt for industrial use, a hose, and a seal or the like.
2. Description of the Related Art
Rubbers having a backbone which comprises a single bond are known to have an excellent thermal aging resistance, and a typical example thereof is an amorphous ethylene-propylene-diene copolymer rubber. This rubber comprises ethylene-propylene as a main component, and a diene such as dicyclopentadiene, ethylidene-norbornene or the like is random copolymerized to permit a crosslinking by sulfur. If a stronger thermal aging resistance is required, however, an amorphous ethylene-propylene copolymer rubber free of such a diene is preferred. In view of vulcanizing factors such as the sulfur used for crosslinking the amorphous ethylene-propylene-diene copolymer rubber, a polysulfide bond in addition to a monosulfide bond may be present in the rubber. Such a polysulfide bond is unsuitable for heat-resistant use because of its low heat-resistance. On the other hand, a vulcanizing agent such as an organic peroxide used in an amorphous ethylene-.alpha.-olefin copolymer rubber, particularly in an amorphous ethylene-propylene copolymer rubber, has an excellent thermal stability because a sigma bonding is formed between molecules. However ethylene-.alpha.-olefin copolymer rubbers still have an unsatisfactory thermal aging resistance or wear resistance as a material of maintenance-free products such as a heat-resistant belt, hose or the like which can be used for a long period without impairing their properties. As a means for solving the problem, an increase of the ethylene content in an amorphous ethylene-.alpha.-olefin copolymer is known, but an amorphous ethylene-.alpha.-olefin copolymer rubber having a high content of ethylene has a remarkably inferior roll processability, and thus is not used in practice for the forming of articles.
Currently, a material having properties antagonistic to each other, such as a high ethylene content and excellent roll processability, is required, but commercially available amorphous ethylene-.alpha.-olefin copolymer rubbers, in particular an amorphous ethylenepropylene copolymer rubber, are now designed with a stress on the roll processability thereof and have a low ethylene content of about 60 mole %, and thus such copolymers have problems with regard to the thermal aging resistance or wear resistance thereof.